The subject invention refers to a solenoid, comprising at least two stationary coils, which are located axially beside each other and are current supplied at the same time, and at least one magnetically active element, such as a permanent magnet or a soft iron part.
Solenoid devices have many different fields of application. They can for instance switch over circuit-breakers or valves. One example of an utmost demanding application is to be used as a fuel valve in a fuel-supply system for an internal combustion engine. The present invention is based on such an application. The valve shall be able to open and close with a frequency of up to 300 Hz, at the same time as its consumption of energy must be low. In the current absence state the valve shall be open, i.e. it shall have one opening position only. Obviously it should also have a simple, cheap, dependable construction.
It is very difficult for a conventional solenoid with a winding and parts of soft iron to fulfill, the outlined claims. It has great inertia, both electrically, by high inductance, and mechanically. Further it has many parts and is relatively complicated GB 1228539 and GB 2228831 show solenoids having two coils located axially beside each other. But these coils are used alternately and therefore no higher power than for the conventional solenoid can be achieved. It is also known to use a movable permanent magnet, which is driven by means of two surrounding and at the same time current supplied coils. The coils are surrounded longitudinally and radially outwards by soft iron parts, which direct the magnetic flow. The coils have opposite current direction, so that they form a mutual pole in the soft iron part, which separates them. These solenoids have a relatively complicated construction since they have soft iron lids in both ends and a soft iron ring in the middle in order to direct the magnetic flow.
GB 1136418, DE 3426688, JP 57-198.611 show examples of this type of solenoids, which have two holding positions when they are not supplied with power. U.S. Pat. No. 4,422,060 shows a solenoid with a holding position. All those have a light-weight permanent magnet, but a complicated magnetic frame, which closes the magnetic flow.
DE 4040120 shows a permanent magnet surrounded by one or two coils. These coils are not at all surrounded by any soft iron parts. The description is very brief, e.and nothing is mentioned about current direction in the coils or how the permanent magnet""s poles are placed. The coils are placed in a relatively large distance from each other. The tuning of the length of the permanent magnet and the coils"" mutual distance is such that one of the ends of the permanent magnet is located in an xe2x80x9cexplosive pointxe2x80x9d and the other one in an xe2x80x9cimplosive pointxe2x80x9d. The description is brief and xe2x80x9cphenomen-accentuatedxe2x80x9d. It seems that the coils have the same current direction and such a large mutual distance, so that their power action on the permanant magnet can be able to cooperate.
The purpose of the subject invention is to essentially reduce the above outlined problems.
The above mentioned purpose is achieved in a solenoid, according to the invention, having one inner and one outer magnetically active element, of which at least one is composed of an essentially axially magnetized permanent magnet, and the coils are located between the elements, so that they surround the inner element, and are arranged with mutually different current direction, and the coils and the elements are arranged around an essentially mutual axial centre line, so that a magnetic field is obtained between the elements and this crosses the current supplied coils"" wire essentially perpendicularly and gives rise to an axial power action between the coils and the elements and at least one of the elements is axially movable. Consequently, the two coils are not surrounded in anal direction by any soft iron parts, which direct the magnetic flow between one inner and one outer magnetically active element. The flow crosses instead the current supplied coils"" wire essentially perpendicularly. Accordingly, by means of this the way of function differs from the majority of known solutions. The magnetic field flows between one outer and one inner magnetically active element, which definitely separates the present invention from DE 4040120, just like the mutually different current direction of the coils. This construction leads to a simple design with very good performance. As the magnetic flow is passing essentially radially between one inner and one outer magnetic element a very good power action is created between magnetic elements and winding As the coils have mutually different current direction the inductance of the solenoid becomes extremely low. This contributes to high rapidity and low consumption. These and other characteristic features and advantages will become more apparent from the detailed description of various embodiments with the support of the appended drawing.